In general, power distribution systems receive high voltage and/or high current electrical power from a utility provider, generator station, or other source of power. The power distribution systems may transform the received power to electrically powered equipment, such as the computers and cooling equipment in a data center. Electrical power is generally conducted by high current conductors that may be split into two or more branch conductors to divide and distribute electrical power. Some of these branches may be split to further divide and distribute electrical power. Each of the electrical conductors may be protected by circuit breakers, and/or other over-current protection devices to stop the flow of electrical currents in excess of the conductors' ratings.
Electrical devices are generally rated for a maximum current draw, and in some instances these ratings can be somewhat conservative. In addition, the electrical devices may only occasionally, if ever, draw their rated currents. In some instances, power distribution systems can be conservatively built to supply the devices' rated currents. The collective power of the devices connected to branches of the power distribution system may remain conservatively below the breaker limit for their respective branch, and the attached devices may not be drawing their maximum amount of power simultaneously. Overall, a power distribution system may leave some portion of the available power unused, and the amount of unusable power may increase as the number of power branches increases.
Operators of data centers also want to protect their electrical devices from black-outs and brown-outs. As a result, such operators may install uninterruptible power supplies (UPS's) that can both condition power and provide some level of battery back-up, either to keep a system operating throughout a power failure, or to give the system enough time to shut down safely and cleanly. In a large computer data center, such a UPS may condition power as it enters the data center, and may condition many megawatts of power.